As regulations on environmental contaminants such as CO2 by the international community have been strengthened and the consumers' demand for a vehicle having high fuel efficiency and output power has increased, the vehicle industry has made significant efforts to develop vehicles with improved fuel efficiency, output, and safety.
Among such efforts, reducing the weight of the vehicle may be obtained by applying a high tensile strength steel sheet having high stiffness which has reduced thickness to the vehicle instead of using a thick common steel sheet for an exterior plate. Accordingly, fuel efficiency output and the like have been improved as well as the safety of the vehicle and the like due to characteristics of high-strength steel sheet.
Typically, the high tensile strength steel sheet applied to vehicles refers to a material having a tensile strength of about 340 MPa level or greater. However, clunking may be produced even at a small pressure exerted on the exterior plate of the vehicle, particularly when the thickness of the high tensile strength steel sheet applied to the exterior plate is reduce. Further, slight noise may be produced due to the thinned high tensile strength steel sheet when the door is opened and closed, and loud rainy sound and the like may be produced, so that significant amount of complaints from customers have been received. In addition, such problem may become greater as the thickness of the high tensile strength steel sheet is reduced.
As such, there is a need to develop a new steel sheet which may have reduced weight and improved strength than a high-tensile strength steel sheet in the related art, may provide solution to the problem of clunking, and also have improved dent resistance and the like, although effects of reducing weight in automobiles deteriorate when the thickness of the high tensile strength steel sheet becomes large.
In order to develop the new steel sheet, methods of laminating polymers between steel sheets have been developed. In the related arts, a multi-layer film and a laminate used in a printed circuit board has been reported and the multi-layer film and the laminate may include: a support layer containing a thermoplastic resin; an adhesive layer containing a polyolefin resin; a metal thin layer; and the like. However, such multi-layer film and laminate has been applied to a circuit substrate.
Moreover, in the related arts, a laminated sheet metal has been developed. The laminated sheet metal includes: a sheet metal; a thermoplastic resin film containing one or more films selected from the group consisting of a polyolefin resin film, a polyamide film, and the like; a primary resin layer; and the like. Although the sheet metal has enhanced corrosion resistance, it may not have sufficient strength for the use in a vehicle.
Accordingly, we now provide new laminated polymers and the like which is formed between steel sheets, thereby providing steel sheet with enhanced strength, reduced weight and the like.
The description provided above as a related art of the present invention is just merely for helping understanding of the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.